Want to install deeper bathtub -- will my floor support it?

Discussion in 'Shower & bathtub Forum & Blog' started by eeka, Mar 1, 2008.

  1. eeka

    eeka New Member

    Messages:
    17
    Location:
    Massachusetts
    Hi, I'm hoping someone here will know where to start to find out this information...

    I'm looking to install a soaking tub in the space currently occupied by my normal bathtub -- thinking about something about 20" deep and acrylic. My question is whether the additional weight of the tub (when full) would be something to be concerned about. I'm seeing specs showing that the acrylic tubs are around 600-700 pounds when filled. Would this be too much weight on my floor? I know that other items in my home (piano, appliances) get up into this weight range, but I'm wondering if there would be a difference in the stress on the floor joists since the tub would go between weighing 100 pounds and weighing 700 pounds several times a week (whereas the other stuff pretty much stays put). The house was built in 1893 and is wood construction. It appears to be pretty solid judging by the huge beams visible in the basement. One thought I had was to assume from the age of the house that there's probably been a heavy cast iron tub at some point, but I also really have no way of knowing if the current bathroom even started out as the bathroom -- maybe the floor is reinforced some places but not others?

    Anyway, is it pretty common to just assume that the house can take the weight of a deep tub and go for it, or should I have someone come check it out? What kind of person would even do such a thing? Structural engineer, or what?

    Thanks!
  2. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,889
    Location:
    New England
    A modern house is designed for about 40#/square foot. Older ones are a crap shoot. Probably won't hurt.
  3. Nate R

    Nate R New Member

    Messages:
    472
    Location:
    Milwaukee, WI
    What's your normal bathtub made of now?
  4. krow

    krow Plumber

    Messages:
    906
    Location:
    Ontario, Canada
    It should be ok. You can distribute the weight if you lay the tub on a motar/concrete bed as your installing the tub
  5. jimbo

    jimbo Plumber

    Messages:
    8,997
    Location:
    San Diego
    Assuming your old tub was cast iron, probably weighed 350+, so right away, the differential between that and the acrylic tub with maybe 5 cubic feet of water more ( about 300 pounds ) you are OK.

    I would be much more concerned about how you will heat the extra 40 gallons of water.


    As far as the structure of the house, scary things are often discovered in old houses, because back in '02 ( that would be 1902!) when the orignal old timers installed the first indoor plumbing, they were notorious for their disrespect for structure! There was no choice for them but to whack the joists to get pipes where they needed to go.
  6. eeka

    eeka New Member

    Messages:
    17
    Location:
    Massachusetts
    The current tub is some sort of porcelain, since it chips like porcelain. It appears to be from the '70s or so based on style. Would it likely have been a solid hunk of porcelain, or porcelain over a frame of metal or something?

    I hadn't thought about the water heater. It seems to be average sized (normal-looking cylindrical thing like you find in most houses). It will let me run the shower for about 45 minutes before it gets cold, and longer if I turn the water heater up all the way. Do people typically install bigger water heaters for this sort of thing? I have noticed that some of the tubs have an integrated heater like in a hot tub, but that tends to be the bigger tubs (I'm looking at the ones that are the size of your usual bathtub, but deep). Thanks!
  7. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,889
    Location:
    New England
    If the tub is cast iron, it will have sort of a metalic thud if you hit it - it's quite heavy and fairly thick. It's possible it is a porcelain over steel...those are thinner and ring higher and you might get it to flex a little.

    A typical WH is rated to provide about 70% of it's volume before the output gets noticably colder than desired. Somewhere on your WH it should indicate the volume. Compare that to your desired tub's volume. Keep in mind that you don't use entirely hot (normally anyways) when filling a tub, so that 70% goes further than just filling the tub. If you raise the temperature of the tank, you can fill a larger tub. You may want to put a tempering valve on the output of the tank to limit the max to prevent scalding.
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